The present invention relates to methods for processing arrays of carbon nanotubes.
Carbon nanotubes were first discovered by S. Iijima (Nature, vol. 354, pp. 56-58, 1991) and were synthesized by T. W. Ebbesen and P. M. Ajayan (Nature, vol. 358, pp. 220-222, 1992). Theoretical studies show that carbon nanotubes exhibit either metallic or semiconductive behavior depending on the radii and helicity of the nanotubes. Carbon nanotubes have interesting and potentially useful electrical and mechanical properties, and offer potential for use in electronic devices such as field emission displays, micro electron sources in vacuum, and nano-scale devices. However, to realize these various potential uses, specific methods for processing arrays of the carbon nanotubes may be necessary.
For example, when arrays of carbon nanotubes are to be used in a field emission display, each array of carbon nanotubes must first be processed. This is because synthesized carbon nanotubes are generally densely configured. In a “raw” array, a shielding effect would unavoidably occur between adjacent carbon nanotubes. If the synthesized array of carbon nanotubes is directly employed as an emitting structure in a field emission display, the field emission performance of the carbon nanotubes may be impaired. Typical methods for processing an array of carbon nanotubes generally include a laser processing method, a plasma processing method, a chemical processing method, etc. These processing methods can reduce the shielding effect, lower a threshold field emission voltage, and improve the field emission performance.
A typical laser processing method was reported in an article by Zhao W J, Kawakami N, and Sawada A et al, entitled “Field Emission from Screen-printed Carbon Nanotubes Irradiated by Tunable Ultraviolet Laser in Different Atmospheres” (Journal of Vacuum Science & Technology B 21 (4), July-August, 2003, pp. 1734-1737). In this method, an array of carbon nanotubes is processed by applying an ultraviolet laser beam with a suitable wavelength and energy density for a suitable period of time. The threshold field emission voltage of a field emitter formed by the processed array of carbon nanotubes is lowered from an original 3.2V/μm to 1.2V/μm. The field emission performance of the field emitter is improved accordingly.
A typical plasma processing method was reported in an article by Kanazawa Y, Oyama T, and Murakami K et al, entitled “Improvement in Electron Emission from Carbon Nanotube Cathodes after Ar Plasma Treatment” (Journal of Vacuum Science & Technology B 22 (3), May-June, 2004, pp. 1342-1344). In this method, an array of carbon nanotubes is processed by an Ar plasma with a discharge voltage of 250 volts, a radio frequency power of 60 watts, and a pressure of 40 Pa. Thus, the threshold field emission voltage of a field emitter formed by the processed array of carbon nanotubes is lowered from an original 3.3V/μm to 1.7V/μm. The field emission performance of the field emitter is also improved.
However, the above-mentioned methods need to employ expensive apparatuses. The cost of processing the arrays of carbon nanotubes via any of the above-mentioned methods is unduly high. In addition, the apparatuses are relatively complicated to operate.
What is needed, therefore, is a method for processing an array of carbon nanotubes which can reduce any shielding effect between adjacent carbon nanotubes and which is simple to implement.